What went up, and by how much
Thames Water's answer on their own charges questions page is short: "For most households, water and wastewater bills increased by an average of 3.4% for 2026-27. This works out to around £2 more per month for most of our customers." The new charges started on 1 April 2026.
The fuller version is in their Statement of Significant Change for the 2026/27 charges schemes, published on 13 January 2026 and signed on 9 January. It is a document written for regulators rather than customers, and it is the only place the movement is broken out properly. Their table of typical bill movements against 2025/26 reads:
| Customer type | Unmeasured | Metered |
|---|
| Water-only | 9.3% | 9.5% |
| Waste-only | (3.7%) | (3.5%) |
| Dual service | 3.4% | 3.4% |
Those are the figures after Thames Water applied part of what they call the Blind Year Adjustment, a £10m reduction to their allowed wholesale water revenue used to hold the increase down. Before it, the same table shows 10.0% for metered water-only customers and 3.7% for metered dual-service. Most London households are dual-service, so 3.4% is the number that describes you. The roughly 50,000 water-only households in their region are the ones carrying a rise above 5%.
What drove it
Thames Water list five things in that statement. Their allowed revenue for 2026/27 was fixed by Ofwat's 2024 price review final determination. That was then adjusted by an in-period determination published on 13 November 2025, reflecting outcome delivery incentive payments tied to their actual performance in 2024/25. On top sits the Thames Tideway Tunnel infrastructure provider charge, which they collect from wastewater customers on behalf of Bazalgette Tunnel Limited. Then inflation, at a CPIH figure of 3.5% taken from the Office for National Statistics release of 17 December 2025. Then forecast changes in how much water households and businesses use.
One line in the same document is worth holding on to, because it disposes of a common suspicion: "There are no significant changes in charging policy from the previous year." Nothing about how you are charged changed in April. The unit price did.
The only numbers a leak cares about
A percentage is a poor tool for thinking about a leak, because a leak is a volume. The volumes are priced on Thames Water's metered customers page, and as of 1 April 2026 they are £2.7346 per cubic metre for clean water and £1.4721 per cubic metre for wastewater. That is £4.2067 per cubic metre of water that goes through your meter, whether it reaches a tap or not.
Fixed charges sit on top and do not move with volume at all: £66.87 for water and £128.13 for wastewater, or £80.43 where the surface water drainage rebate applies. Leave them out of any leak arithmetic, because a leak does not change them.
Thames Water give the conversion themselves: "One cubic metre equals 1,000 litres which is an estimated 25 quick showers."
Typical bills, before and after
The same company publishes a typical annual metered bill table on its metering programme page, for both charging years. For a household they class as medium use — washing machine and dishwasher on most days, longer showers — it runs:
| Occupants | 2025-26 | 2026-27 |
|---|
| 1 | £438 | £450 |
| 2 | £600 | £619 |
| 3 | £756 | £782 |
| 4 | £860 | £891 |
| 5 | £1,027 | £1,066 |
| 6 | £1,172 | £1,218 |
So for a three-person household at medium use, the whole of this year's increase is £26.
Now put a leak underneath it
Thames Water cost three grades of leaking toilet on their identifying leaks page, and the figures are theirs, not ours. A small trickle wastes up to 200 litres a day and costs an extra £161.33 a year. Rippling water wastes around 600 litres a day and costs £483.99 a year. Water flowing constantly can waste 8,000 litres a day and cost £6,453.20 a year.
Set that against the £26. The rippling loo is about eighteen times this year's increase, on the same company's numbers. The constantly flowing one costs more in a year than the highest household in their own typical bill table pays for everything, at any level of use.
A leaking toilet is also the cheapest of these problems to fix, which is the point of putting it first. The expensive version is the one you cannot see: a pinhole in a supply pipe under a front path, running twenty-four hours a day into ground that swallows it without a mark. That is on the same meter and the same tariff, and it does not announce itself. Working out what a leak costs you per day is the arithmetic in full.
Why you may not notice for six months
Thames Water bill metered households twice a year: "We'll send you a bill every six months." They also warn that metered customers paying by instalments may see those instalments go up, for several reasons at once — the tariff, the estimate of your usage, and any balance being recovered.
That billing rhythm is the reason leaks get expensive rather than the reason they start. A pinhole that begins in October on a six-monthly cycle can run to April before a bill arrives showing it, and the bill that arrives will be partly estimated, which blurs the signal further. If you pay by a level direct debit, the first thing you are likely to see is not a shocking bill at all but a letter saying your monthly payment is being increased, which is easy to file and forget.
Submitting your own readings breaks that. A reading every month takes two minutes and turns a six-month surprise into a four-week question, and it is also the evidence base any allowance claim is later built on.
Where the money goes, in their account of it
Thames Water publish a breakdown of every pound: 55p on infrastructure, 37p on day-to-day services including energy, rates and salaries, and 8p on financing the money they borrow. They also state that they have paid no dividends to shareholders since 2017, and describe a record £20 billion investment programme, more than double what they invested between 2020 and 2025, covering replacing "hundreds of miles of ageing and leaky pipes" and installing over one million smart meters.
Whether that is good value is not a question an engineer can settle. What it does tell you is the direction of travel: more metering, more detection, and an operator with a strong interest in knowing exactly how much water crosses your boundary.
If the bill jumped and you do not know why
Do the meter test before anything else. Close the internal stop valve, take a reading, wait half an hour with nothing drawing water, read again. A rise means the loss is outside on the supply pipe; no rise means it is inside the house. Reading the meter properly takes half an hour and costs nothing, and it is the step that decides whether anyone needs to attend at all.
If you have a smart meter, look for the overnight baseline in your online account. A house with nothing running should drop to a flat nothing between about two and five in the morning. A floor that never reaches zero is the signature of a continuous loss.
When not to call us
If your usage explains the bill — a new occupant, a hot summer, a filled paddling pool, a builder on site — there is nothing to find. If you are unmetered, your bill moves with your property's rateable value and not with a leak at all, so a rise this April is the tariff and nothing else. If you are struggling to pay, Thames Water's statement describes WaterSure and WaterHelp, with new WaterHelp discount tiers of 25%, 75% and 99% added alongside the existing 50% for 2026/27, plus an Extra Support Scheme bill credit for customers in arrears with a household budget deficit. Ask them before you pay anyone.
Call us when the meter says water is leaving and nobody can say where. Our work is £150 per hour, agreed before we attend, and if we do not find the leak you do not pay for the time we spent looking. Pricing is one page. Supply pipe work and the making good afterwards are the same firm.
